1. Field of the Invention
The present invention relates to a reproducing apparatus, particularly relates to the apparatus which reproduces an information signal recorded on a recording medium.
2. Description of the Related Art
In recent years, greater density and larger capacity in a disk-shaped recording medium are rapidly proceeding. A recording and reproducing apparatus in which not only a sound signal but also a still image signal or moving image (video) signal can be finely recorded for long time on the disk-shaped recording medium and a recording signal can be reproduced from the disk-shaped recording medium has been proposed.
In such recording and reproducing apparatuses, since a size of the disk-shaped recording medium itself is being miniaturized, compared with the conventional recording and reproducing apparatus using a tape-shaped recording medium, further miniaturization has been achieved, rapid and random data-access advantage has been realized, and remarkable improvement in functions with respect to easy portability of the disk-shaped recording medium, high reliability, low cost, search readiness in operation, and the like has been accomplished.
Reproducing operation of the recording and reproducing apparatus using the conventional disk-shaped recording medium will be described below referring to FIG. 15. In FIG. 15, a reproduction trigger unit 1101 outputs a reproduction start instruction in response to user's operation. Then, in a mechanical servo control unit 1102, access processing such as seek to a target address on the disk-shaped recording medium is performed by servo mechanism control on the basis of the reproduction instruction. In advance to the reproduction, a reproduction parameter setting unit 1103 optimizes such a reproduction parameter such as reproducing laser power on the like. A data detection unit 1104 performs such processing as predetermined gain control, waveform equalization, digitalization, and clock extraction on the reproduced data. A demodulation ECC unit 1105 performs error correction on the reproduced data after performing predetermined demodulating processing.
After the error correction processing, the reproduced data is sequentially written into a memory 1106. The data is read out from the memory 1106 at a rate slower than writing rate and transmitted to a decoder 1107 of the next stage.
Access operation to the memory 1106 will be described below referring to FIG. 16. FIG. 16 shows time-progression of the amount of data in the memory 1106 and write and readout timing signals. After the reproduction trigger unit 1101 outputs the reproduction instruction at a time t0, the data is written in the memory 1106 between a time t1 and a time t2. The data readout from the memory 1106 is started at the time t2 when the data is accumulated up to a predetermined memory amount “a”, and the data readout is continued until a time t3 when the data reaches to a predetermined memory amount “b”. Then, the processing, in which the data is written between the time t3 and a time t4 and the data is read out between the time t4 and a time t5, is repeated.
The decoder 1107 expands and decodes compression encoded data which is read out from the memory 1106. A video output processing unit 1108 converts the decoded data into a video signal pursuant to a predetermined output format and outputs the video signal to a display system or an external signal terminal.
As described above, the reproducing processing sequentially proceeds after receiving the reproduction start instruction in the reproducing operation of the conventional recording and reproducing apparatus using the disk-shaped recording medium. However, it considerably takes time to output actually the desired video image. Physical access time to the disk-shaped recording medium by using the mechanical servo control, and buffering time in which an intermittent and high-speed read signal obtained from the disk-shaped recording medium is temporarily stored and decoded at a predetermined transmission rate, are main factors of such the waiting time.
Some proposals for decreasing the waiting time in the reproducing operation have been made. For example, in Japanese Patent Application Laid-Open No. H08-194982, there has been made the proposal which decreases the physical access waiting time in such a manner that individual memory spaces are previously secured for a plurality of the information data recorded on the disk-shaped recording medium respectively, the reproduced data having a certain quantity from a front end is accumulated in the memory space, and the selected information data is read out from the memory in response to the reproduction start instruction.
In Japanese Patent Application Laid-Open No. H11-296862, there has been made the proposal which decreases the buffering waiting time by monitoring an amount of write data into the memory and outputting the data from the memory at a time when the minimum data required for the reproduction is secured.
However, even if configurations described in Japanese Patent Application Laid-Open No. H08-194982 and the like are applied to the conventional recording and reproducing apparatus, there are the following problems in the conventional recording and reproducing apparatus.
At first, when the data recorded on the disk-shaped recording medium is the long-time moving image data, unlike music data, a specific start position such as “the front end of a piece of music” can not be previously designated. Further, as the larger capacity of the disk-shaped recording medium proceeds, the conventional recording and reproducing apparatus could not deal with a situation in which the enormous amounts of data to be previously secured in the memory have swelled.
When writing the data in the memory and reading the data from the memory are dynamically controlled as taught by Japanese Patent Application Laid-Open No. H11-296862, it can not be avoided that quality in buffering function with which the apparatus should be primarily provided is degraded. That is to say, for disturbance such as shock and vibration which are unavoidable for the use of the apparatus in mobile environment, shock-proof function maintaining the continuousness of the data is forced to be traded off for decreased waiting time. Particularly, even if the speed-up is attained only by focusing on readout timing, the problems such as speed-up of the physical access to the disk-shaped recording medium and other functions still remain.